The subject matter of my earlier U.S. Pat. No. 4,950,290 granted on Aug. 21, 1990 and entitled POSTERIOR CHAMBER INTRAOCULAR LENS, and U.S. Pat. No. 6,282,449 granted on Aug. 28, 2001 and entitled IMPROVED METHOD AND DEVICE FOR CAUSING THE EYE TO FOCUS ON A NEAR OBJECT are incorporated in their entirety into this patent application.
Typically, the eye focuses on a near object by increasing the curvature of the lens. The change in curvature is called “accommodation.” The objective of accommodation is to sharply focus an observed image on the retina.
The curvature of the lens is controlled by the circular fibers of the ciliary muscle. The ciliary muscle is an annulus that is connected to the lens by the zonules. When the ciliary muscle is relaxed the lens is flattened, i.e., it has less curvature. Thus distant objects are in focus.
Contraction of the ciliary muscle causes the zonules to relax and the lens to thicken, i.e., it has more curvature, thereby shortening its focal distance to accommodate the viewing of a near object.
Described in my earlier U.S. Pat. No. 6,282,449 is a method and device for dealing with the presbyopia of a natural lens. Thus, an aging natural lens becomes hardened and the ciliary muscle weakens thereby precluding or diminishing the ciliary muscle's ability to change the curvature of the lens so that the person will be able to focus on near objects.
However, the method and device described in U.S. Pat. No. 6,282,449 is not suitable when a non-accommodating intraocular lens replaces the natural lens such as after the removal of cataracts.
In my earlier U. S. Pat. No. 4,950,290 there is disclosed an intraocular lens and a method for implanting it in the posterior chamber. The lens described in that patent comprises an optic disc which is supported by a haptic which extends between the optic disc and the tissue supporting it to retain the optic disc in the desired location on the visual axis in the posterior chamber.
The use of a haptic to support an optic disc is well known. Haptics are discussed extensively in Eye World, Vol. 7, No. 8; August 2002; pgs. 30–34.
However, while haptic based intraocular lenses are well known, most have not been capable of accommodation. Further, because of the space required for the haptic in accommodating intraocular lenses, the optic discs of the prior art are no more than about 4.50 to 5.50 millimeters in diameter. With optic discs of such small diameter, several negative effects can occur. Thus, it is common for patient to see halos or to be annoyed by glare around the edge of the optic disc. Further, it is relatively easy for a small optic disc to become decenterd thereby diminishing its effectiveness or making it useless.
It is desirable to have an intraocular lens that can automatically accommodate to bring near objects into focus in response to contraction of the ciliary muscle as described in my earlier U.S. Pat. No. 6,282,449.
Further, it would be especially advantageous if such an intraocular lens were progressively multi-focal so as to avoid the need for wearing trifocal eyeglasses.
These objectives and advantages can be achieved by taking advantage of the fact the contraction of the ciliary muscle actually tends to reduce the volume of the posterior compartment slightly. Since the volume of the vitreous humor in the posterior compartment can not be reduced, it presses against the posterior capsule 16 and moves it slightly anteriorly.
It has been discovered that the vitreous humor can be used to cause relative movement between two parts of an intraocular lens assembly that is placed in the capsular bag so the eye focuses by moving the optic anteriorly (toward the near object) to focus instead of changing its curvature as disclosed in my U.S. Pat. No. 6,282,449. When focusing on a far object the ciliary muscle relaxes and the optic can move posteriorly to return to its previous position relative to the retina.